This invention relates to a governor for use in controlling the operation of a diesel engine. The invention is particularly applicable to engines used to drive alternator sets.
It is known to provide a mechanical governor to control the rate at which fuel is supplied to a compression ignition internal combustion engine for driving an alternator set, thereby permitting the alternator set to be driven at a substantially constant speed irrespective of the load on the engine. Such a governor typically comprises a plurality of weights which are pivotally mounted upon a drive shaft driven at a speed associated with the output speed of the engine. Typically, six weights are provided. The weights act upon a lever which is moveable against the action of a return spring. The lever is coupled to a metering valve of a fuel pump for use in supplying the engine with fuel under high pressure. The governor is arranged such that, in use, if the load on the engine falls, then the engine operating speed will increase. Such an increase in engine speed will cause the weights to pivot outwardly as a result of an increase in the magnitude of the centrifugal force acting upon the weights. The movement of the weights causes the lever to move, the movement of the lever, and hence the weights, occurring against the action of the return spring. The movement of the lever is transmitted to the metering valve, adjusting the metering valve to restrict the supply of fuel to the engine and reduce the engine speed. Similarly, a reduction in engine speed will cause the governor to operate to increase the rate at which fuel is supplied to the engine.
A governor is usually designed to operate at a chosen speed, for example to cause the engine to drive an alternator set at 50 Hz or 60 Hz. Modification of a governor intended to operate at a first speed to operate at a second speed may require the throttle to be moved through a large distance, and the droop of the governor will not be constant at both speeds. Rather than adjust the position of the throttle, it is known to replace the governor spring or to modify the rate of the spring in some way.
It is an object of the invention to provide a governor, the operating speed of which can be adjusted without requiring the replacement of parts of the governor and without requiring a significant adjustment of the throttle position.
According to the present invention there is provided a governor comprising a drive shaft, a plurality of weights carried by the drive shaft, the weights being rotatable with the shaft and being moveable relative to the shaft, a lever moveable in response to movement of the weights, the lever being moveable against the action of return biasing means, and means whereby at least one of the weights can be held against movement to adjust the operating speed of the governor.
Conveniently, the weights may be pivotally moveable relative to the shaft, at least one of the weights being held against pivotal movement to adjust the operating speed of the governor.
Conveniently, six weights are provided, the weights and the return spring being chosen such that the governor operates at an alternator speed of 50 Hz. The governor is conveniently arranged such that two of the weights can be held against pivotal movement, under which circumstances the governor will operate at an alternator speed of approximately 61.2 Hz, and only a slight adjustment of the throttle will be necessary to ensure that the governor controls the associated engine to operate at an alternator speed of 60 Hz.
As there is no need to move the throttle through a large angle, the droop of the governor is not significantly altered when the governor is modified to operate at an alternative speed. Further, there is no need to replace components of the governor in order to change the operating speed.
The governor preferably includes a cage which is rotatable with the drive shaft, the weights being housed within the cage.
The weight(s) may be held against pivotal movement by, for example, wedges or pins, by jacking, by the use of pinch bolts, by use of a sliding collar or by any other suitable arrangement. For example, the governor may comprise at least one pin associated with each weight to be held against movement, whereby the or each pin cooperates with the cage to hold the associated weight against movement. Alternatively, a collar may be provided, the collar being slidably movable with respect to the drive shaft between an operative position, in which at least one of the weights is held against movement, and an inoperative position in which the weights are free to move.
Preferably, the return biasing means take the form of a return spring.
Conveniently, adjustment of the governor operating speed can be achieved without disassembling the pump housing, the adjustment being achieved, for example, by inserting a suitable tool through the pump housing drain port.